Selective Electrooxidation of Glycerol Into Value-Added Chemicals: A Short Overview

A comprehensive overview of the catalysts developed for the electrooxidation of glycerol with the aim of producing selectively value-added compounds is proposed in the present contribution. By presenting the main results reported in the literature on glycerol electrooxidation in acidic and alkaline media, using different kinds of catalytic materials (monometallic catalysts based on platinum group metals and non-noble metals, multimetallic alloys, or modification of surfaces by adatoms, etc.) and under different experimental conditions, some general trends concerning the effects of catalyst composition and structure, of reaction medium and of the electrode potential to enhance the activity for the glycerol oxidation reaction and of the selectivity toward a unique value-added product will be presented and discussed. The objective is to provide a guideline for the development of electrochemical systems which allow performing the electrooxidation of glycerol at the rate and selectivity as high as possible

Production of Clean Hydrogen for Fuel Cells by the Electrochemical Decomposition of Organic Compounds in a Proton Exchange Membrane Electrolysis Cell (PEMEC)

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Préparation et caractérisations physicochimiques de nanoparticules de platine à distributions de taille et de forme contrôlées

Des nanoparticules de platine non supportées ont été préparées par différentes voies de synthèses colloïdales. Les méthodes mises en œuvre ont permis d obtenir une collection d objets de forme variable dans une gamme de taille nanométrique. Différentes techniques de caractérisations ont été utilisées pour la détermination de paramètres comme la taille et la forme (microscopie) ou encore la structure superficielle (électrochimie) des nanocristaux. Ainsi, il a été démontré que les nanoparticules préparées exposent des fractions variables de surface orientées (111) et (100) et de défauts en accord avec leurs formes. L étude de nanoparticules de platine de formes contrôlées apparait aujourd hui comme le lien manquant entre les catalyseurs industriels et les surfaces monocristallines. La réaction d électro-oxydation du monoxyde de carbone a été étudiée afin d apporter des informations sur les mécanismes mis en jeu à la surface des nanoparticules. Les résultats obtenus mettent clairement en évidence une forte dépendance du signal électrochimique et plus précisément du potentiel d oxydation à la structure superficielle exposée par les nanoparticules. Enfin, la possibilité d un nouveau mécanisme à plus bas potentiel sans adsorption dissociative de l eau a aussi été mise en avant.Unsupported platinum nanoparticles were prepared by using some different colloidal synthesis procedures. These methods lead to the preparation of a collection of object including a wide range of shape in nanometric scale. Size and shape of nanocrystals were determined by microscopy while superficial structure was obtained by electrochemical methods. It was evidenced that platinum nanoparticles expose variable fractions of surface oriented domains (111) or (100) and defect sites in agreement with the observed shapes. Study of well-defined shaped nanoparticles now appears as the missing link between carbon supported platinum nanoparticles and platinum single crystal surfaces. Carbon monoxide electro-oxidation was studied on these samples in order to give some information about the mechanisms occurring at nanoparticles surface. Results point out a strong effect of the superficial structure of platinum particles on the voltammetric signal and particularly the oxidation potential. Finally, another oxidation mechanism not involving water dissociative adsorption is supposed to occur at lower potential.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Determination of the mechanisms of electrocatalytic reactions by combining electrochemical methods and in situ spectroscopy

International audienceMany electrochemical reactions of technical interest (fuel cells, electrolyzers, etc.) need the development of efficient catalysts to increase the reaction rate and selectivity. In order to find new electrocatalysts it is of prime importance to elucidate the reaction mechanisms by identifying the different intermediates involved and elucidating their role in the rate determining step (r.d.s.). Apart from the hydrogen oxidation and evolution reactions, the mechanisms of which are thoroughly established, the oxygen reduction (ORR) and evolution reactions (OER), or the oxidation of low weight alcohols in a Direct Alcohol Fuel Cell (DAFC), are relatively complex since they involve multi electron transfer with the formation of several adsorbed intermediates and reaction by-products. The reaction rate of ORR is very low and it is the main cause of energy efficiency limitation in a Polymer Electrolyte Fuel Cell (PEFC) [1-3]. Alcohols (particularly methanol and ethanol) are of great interest as liquid fuels in a DAFC [4–10], but a rather poor kinetics of their electroxidation is observed with platinum, the only catalyst activating the C–H bond cleavage at ambient temperatures. The adsorption and oxidation of methanol and ethanol on a Pt electrode lead to the formation of poisoning species (mainly adsorbed CO), as observed by in situinfrared reflectance spectroscopy [11-12]. In both cases, the formation of such poisoning species leads to a poor electrocatalytic activity, and the challenge is to enhance the activity of platinum by avoiding the formation of poisoning species through the development of bimetallic or multi-metallic platinum-based electrocatalysts. The elucidation of the reaction mechanisms needs the use of different spectroscopic and analytical techniques under electrochemical control, i.e. the combination of electrochemical methods with other physicochemical techniques. This allows identifying the nature of adsorbed intermediates, the structure of adsorbed layers, the nature of the reaction products and by-products, etc., and determining the amount of these species, as a function of the electrode potential and experimental conditions. This will lead to a deep understanding of the reaction mechanisms, which are depending on the nature of the catalyst, the composition and structure of the electrode. In this communication we will present spectro-electrochemical methods (Infrared Reflectance Spectroscopy [13], Electron Spin Resonance Spectroscopy [14] and UV-visible Reflectance Spectroscopy [15]) able to identify in situthe adsorbed species and reaction products involved in electrochemical reactions of great interest for energy conversion. For the ORR, the comparison of electrochemical data from rotating disc electrodes with results from spectroscopic methods gives information on the reaction mechanism. For alcohol electroxidation reactions, the coupling of electrochemical measurements with Infrared Reflectance Spectroscopy allows the identification of the intermediate species and reaction products as a function of the electrode potential and of its structure. This allowed proposing mechanisms for the reactions involved in electrochemical reactions encountered in the development of Fuel Cells or Electrolyzers: the Oxygen Reduction Reaction and the electroxidation of some alcohols (methanol, ethanol, ethylene glycol, and glycerol). References : [1] G. J. K. Acres, J. C. Frost, G. A. Hards, R. J. Potter, T. R. Ralph, D. Thompsett, G. T. Burstein, G. J. Hutchings, Catal. Today, 38 (1997) 393-400. [2] T.R. Ralph, M.P. Hogarth, Platinum Metals Rev., 46 (2002) 3-14. [3] C.-C. Yang, Int. J. Hydrogen Energy, 29 (2004) 135-143. [4] C. Lamy, A. Lima, V. Le Rhun, F. Delime, C. Coutanceau, J.-M. Léger, J. Power Source,s 105 (2002) 283-296. [5] E. Peled, T. Duvdevani, A. Aharon, A. Melman, Electrochem. Solid State Lett., 4 (2001) A38-A41. [6] C. Lamy, J.-M. Léger, S. Srinivasan, Direct Methanol Fuel Cells: From a twentieth century electrochemist’s dream to twenty-first century emerging technology, in "Modern Aspects of Electrochemistry", J.O’M. Bockris and B.E. Conway (Eds.), Vol. 34, Plenum Press, New York, 2000, Chapter 3, pp.53-118. [7] C. Lamy, E.M. Belgsir, J.-M. Léger, J. Appl. Electrochem., 31 (2001) 799-809. [8] T. Iwasita-Vielstich, in Advances in "Electrochemical Science and Engineering", H. Gerischer and C.W. Tobias (Eds.), Vol.1, VCH Verlag, Weinheim, 1990, p. 127. [9] A. Hamnett, Catal. Today 38 (1997) 445-457. [10] K. Y. Chan, J. Ding, J. W. Ren, S. A. Cheng, K.Y. Tsang, J. Mater. Chem., 14 (2004) 505-516. [11] B. Beden, F. Hahn, S. Juanto, J.M. Léger, C. Lamy J. Electroanal. Chem., 225 (1987) 215. [12] J.M. Perez, B. Beden, F. Hahn, A. Aldaz, C. Lamy, J. Electroanal. Chem., 262 (1989) 251. [13] B. Beden, C. Lamy, Infrared reflectance spectroscopy, in "Spectroelectrochemistry - Theory and Practice", R.J. Gale (Ed.), Plenum Press, New York, 1988, Chapter 5, pp. 189-261 [14] P. He, C. Cha, P. Crouigneau, J.M. Léger, C. Lamy, J. Electroanal. Chem., 290 (1990) 203. [15] O. El Mouahid, A. Rakotondrainibe, P. Crouigneau, J.M. Léger, C. Lamy, J. Electroanal. Chem., 455 (1998) 209

Electroreforming of glucose/xylose mixtures on PdAu based nanocatalysts

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Green Synthesis and Modification of RuO2 Materials for the Oxygen Evolution Reaction

Ion exchange method as a green synthesis route is proposed to prepare hydrous ruthenium oxide nanoparticles (H-RuO 2). Calcination of H-RuO 2 at 350 °C resulted in the crystalline rutile RuO 2 nanoparticles (C-RuO 2). Treatment of H-RuO 2 with 20 vol% ammonium hydroxide solution under microwave irradiation and calcination at 350 °C resulted in a highly electrocatalytic active crystalline RuO 2 nanoparticles (A-C-RuO 2). Electrocatalytic performances of H-RuO 2 , C-RuO 2 and A-C-RuO 2 for the oxygen evolution reaction in 0.50 mol L −1 H 2 SO 4 medium are evaluated and compared. Improved performances towards the oxygen evolution reaction are observed for A-C-RuO 2 when compared to C-RuO 2. Based on XRD, TEM, XPS and Raman characterizations performed on all the specimens, it is deduced that the physicochemical properties (crystallinity, mean crystallite size, level of hydrous rutile content) are varied for A-C-RuO 2 when compared to C-RuO 2. Structure-property correlation has been established to describe the higher electrocatalytic activity of A-C-RuO 2

Electrocatalytic behaviour towards oxygen reduction reaction of carbon-supported Pt x M y Au z (M = Ni, Cu, Co) binary and ternary catalysts

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Modification de supports carbonés pour catalyseurs de pile à combustible par greffage de molécules à propriétés spécifiques

La modification de supports carbonés par des fonctions chimiques affecte notablement les propriétés de surface du matériau de départ. Celle-ci peut être menée par différentes méthodes : oxydation du support, ou greffage par réduction d'un synthon. Cette dernière méthode permet de conserver l'intégrité du substrat carboné, et semble de ce fait plus attractive. La réalisation de couches greffées de molécules sur une surface de carbone est effectuée par réduction d'ions diazonium ou iodonium. Cette réduction aboutie à la formation de radicaux, qui vont, au contact de surfaces carbonées, établir des liaisons covalentes avec le support. En sélectionnant judicieusement les fonctions terminales des groupements greffés, il est possible d'influer sur le comportement des couches actives de PEMFC, tel que le caractère hydrophile/hydrophobe, l'interaction platine/support ou encore l'attribution de caractéristiques de conduction ionique. Dans ce contexte, des couches greffées de groupements thiophénol ont été réalisées afin de renforcer l'accroche des nanoparticules de platine au support ; une limitation du processus de migration des nanoparticules ayant lieu avant le phénomène de frittage a été observée. Des carbones fonctionnalisés par des groupements acide 4-benzènesulfonique et 4-(trifluorométhyle)phényle ont été utilisés dans le but d'augmenter ou de diminuer la mouillabilité des couches actives. Enfin la possibilité de greffer des chaînes alkynyle ouvre la voie à l'attribution de caractéristiques de conduction ionique dans le but d optimiser l'utilisation du catalyseur au sein des couches actives.The modification of carbon substrates by chemical functions significantly affects the surface properties of the material. These changes can be carried out by different methods: oxidation of the support, or grafting of molecules by reduction of a synthon. This last method seems more attractive because it helps to maintain the integrity of the support. The realization of grafted layers on carbon surface is carried out by reduction of diazonium or iodonium ions. This reduction results in the formation of radicals, which react with carbon surface to form a covalent bond. This method allows grafting a large variety of molecules; by selecting appropriate terminal groups it is possible to change different characteristics of the active layer of PEMFC electrodes, such as the hydrophobic / hydrophilic properties, platinum / support interactions and ionic conductivity. In this context, thiophenol grafted layers were realized to strengthen the anchorage of platinum nanoparticles on carbon support, limiting the migration of nanoparticles in course of sintering process. Carbon functionalized with benzenesulfonic acid groups and trifluoromethylbenzene groups were used to adjust the wettability of active layers, in order to improve water management in fuel cells. Grafted layers of alkynyl groups with ionic end functions could also be performed to confer ionic conductivity (protons or hydroxyls) to the catalyst support, in order to improve the use of catalyst in fuel cell electrodes.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Pd-Shaped Nanoparticles Modified by Gold ad-Atoms: Effects on Surface Structure and Activity Toward Glucose Electrooxidation

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Catalyseurs alternatifs pour cathodes de micropiles à combustion directe de méthanol

Les micro-DMFCs pour lesquelles la membrane est de faible épaisseur sont très sensibles au phénomène de crossover. Ce travail est orienté vers une solution qui consiste à utiliser un catalyseur pour la réduction de l'oxygène totalement insensible à la présence de méthanol : la phtalocyanine de fer. L'étude électrochimique de ce catalyseur a permis de mesurer son activité catalytique, de démontrer sa totale insensibilité à la présence de méthanol et sa sélectivité vis-à-vis des produits de la réduction de l'oxygène. Cependant, l'activité catalytique de la phtalocyanine de fer se dégrade lors de la réduction de l'oxygène en milieu acide. Une étude par spectroscopie infrarouge in situ a permis de démontrer que le mécanisme de dégradation du catalyseur est une substitution de l'ion central par deux protons. La connaissance précise de ce mécanisme a rendu possible l'intégration de la phtalocyanine de fer dans une DMFC et un comportement catalytique stable a alors pu être observé.The crossover is a major problem for the development of micro-DMFCs for which the membrane is thinner than for traditional systems. The solution studied in this work consists in using a catalyst for the oxygen reduction reaction tolerant to methanol: the iron phthalocyanine. The electrochemical study of this catalyst enabled to measure its catalytic activity, to demonstrate its total insensitivity to methanol and its selectivity with respect to the products of the oxygen reduction. However, the catalytic activity of the iron phthalocyanine decreases during the oxygen reduction in acid medium. It was possible to show by an in situ infrared spectroscopy study that the degradation mechanism is a substitution of the central ion by two protons. The precise knowledge of this mechanism enabled the integration of the iron phthalocyanine in a DMFC and a stable catalytic behavior could be observed.POITIERS-BU Sciences (861942102) / SudocSudocFranceF